As a Roblox developer, it is currently difficult to work with ReplicatedFirst due to it disabling the default loading screen after 5 seconds, forcing developers to implement a replacement so partially-loaded geometry won’t be exposed if loading takes too long.
A ham-fisted way to test this is to enable Network Simulator right after a local server starts, as that causes all clients to get stuck in loading limbo indefinitely:
After ~10 seconds with empty ReplicatedFirst
10 seconds with something in ReplicatedFirst
This forces developers to have a custom loading screen fallback if they use ReplicatedFirst for anything. In my case, I only wanted to implement a short UI transition between the end of the default loading screen and my game’s lobby. With this behavior, I’m forced to make an entire loading screen from scratch.